Separator of the semipermeable membrane type

ABSTRACT

A separator is provided that is particularly suited for separating gases from liquids by selective diffusion through a semipermeable membrane. The membrane forms an enclosure into which diffusate passes and is attached to a flat portion on a surface of a supporting core, so that a strong and leaktight flat seal between the membrane enclosure and the core is formed, with the enclosure interior communicating with a discharge passage in the core. A valve is provided for shutting off flow through the core whenever diffusate flow rate or viscosity exceeds a predetermined maximum.

[ 51 June 13, 1972 United States Patent Gross Austin et 78 66 99 11 WW 198 79 1 2] 5O 33 I mm a o w f yu NNS O 6 9 l 2 l 2 6 1 3 6 2 210/321 X210/321 ...2lO/487 X Robert 1. Gross, Roslyn Hgts., N.Y.

Pall Corporation, Glen Cove, NY.

Feb. 13, 1970 [73] Assignee:

[22] Filed:

Primary Examiner-John Adee Attorney-Janos & Chapman [21] Appl. No:

ABSTRACT A separator is provided that is particularly suited forseparating gases from liquids by selective diffusion through asemipermeable membrane. The membrane forms an enclosure into whichditfusate passes and is attached to a flat portion on a surface of asupporting core, so that a strong and leaktight flat seal between themembrane enclosure a nd the References cued core is formed, with theenclosure interior communicating with a discharge passage in the core. Avalve is provided for sate flow rate UNITED STATES PATENTS shutting offflow through the core whenever diffu or viscosity exceeds apredetermined maximum.

210/487 X ........2l0/321 Kamrath .,..........................210/487 X21 Claims, 6 Drawing figures Newby et a1.

v 21v W931i a PATENTEDJUH 1 3 I972 SHEET 2 [IF 2 iiri brane as a resultof a positive fluid pressure differential across I the membrane.

Processes of this nature and the devices associated therewith have hadparticular application in desalinating salt water and removingimpurities from blood, and can be used for removing air from oil andhydraulic fluids.

In such systems, there is no substantial fluid flow through themembrane. The fluid carrying the impurities passes over one surface ofthe membrane while either the impurities or impurity-free fluiddiffusethrough to the other side. Normally, in semipermeable membraneseparation processes, the rate of diffusion through the membrane isslow, and the diffusate upon reaching the other side is taken up in acarrier fluid which is discharged at a low flow rate.

In order to improve the rate and efficiency of separation, a largemembrane surface area can be provided. A thin membrane is desirable,since the thinner the membrane, the more rapid the rate of diffusionthrough it. A large surface area also permits a greater diffusion rate.In order to provide a large surface area in a small space, the membranecan be spirally wrapped about a core, through which the diffusate iswithdrawn. The core acts as a support for the structure, but due to thefragility of the membrane, it is not easy to form a durable leaktightseal between the membrane and the core. Consequently, core-type membraneseparators heretofore provided have had a short life.

The sealing problem is complicated by the fact that such membraneseparators often are subjected to high pressure differentials, and wideranges of temperatures. For example, a membrane separator employed inthe hydraulic system of an airplane to remove air must withstandpressure differentials as high as 250 psi. and in some cases as high as3,000 psi. Furthermore, such assemblies are often subjected to atemperature range of 65 F. to 275 F. during operation of the plane, andmust carry high oil flow volumes, of the order of 5 gpm. over themembrane surface. Leakage rates greater than 1 cc. per hour at the highflow rates through such systems could rapidly deplete the system of oiland are therefore not tolerable. Under such circumstances, it can beappreciated that all seals of the membrane must be completely leaktightsince the membrane has some small oil permeability.

Resin bonding agents have been employed to form a leaktight seal to thecore, but have not proved to be a complete answer to the problem. It isdifficult to form leaktight bonds between the membrane and cores made ofmetal, since resins do not adhere well to both metal and the membranematerial. Furthermore, many resins which would otherwise be suitable maybe deleteriously affected by fluids used in the system.

U.S. Pat. No. 3,367,504 to Westmoreland discloses a semipermeablemembrane composite coiled about a core. The core is cylindrical, and themembrane composite is bonded to the cylindrical core by epoxy resin. Oneedge of one of the membranes of the composite is bonded axially to thecore, on one side of the core apertures, and an edge of another membraneof the composite is bonded axially along the other side of the coreapertures, so that the core apertures communicate with the space betweenthe membranes. Such a bond cannot be leaktight, since any relativemovement of the core and the membranes will tend to break the seal.Moreover, all strain of the bond is taken up at the line contact betweenthe membrane edges and the core.

Newby et al., U.S. Pat. No. 3,397,790, show that a membrane compositecan be threaded through slots in a hollow core, and so deliver fluidinto the core. However, although Newby et al. seal the edgesof thesheets together, they do not seal the membrane sheets to the core, andthus leakage can occur.

Merten, U.S. Pat. No. 3,386,583, discloses a membrane enclosure in whichthe core extends into the enclosure. However, with such a configuration,it is extremely difficult to form a leaktight seal at the point at whichthe core emerges from the enclosure.

This invention provides a separator of the semipermeable membrane typein which a leaktight seal is provided between the membrane and the corethat is extremely resistant to high pressure and temperatures, so as toperform satisfactorily for long periods of time under adverseconditions.

The semi-permeable membrane separator of the invention comprises, incombination, a semi-permeable membrane enclosure having a spacetherewithin for flow of material passing into and through the membrane;a core having a flat portion supporting the membrane enclosure: and apassage through the core in fluid communication with the membraneenclosure at the flat portion for discharge of material from themembrane enclosure, the membrane enclosure being attached to the flatportion of the core in a leaktight seal.

A preferred embodiment of the separator of the invention comprises, incombination, a core having a flat portion on the exterior surfacethereof, and a fluid passage therethrough; an opening in the flatportion communicating with the fluid passage; and a semi-permeablemembrane enclosure having an opening therein in fluid communication withthe core opening, and secured in a leaktight seal against the flatportion of the core.

This invention further provides a semi-permeable membrane separatorassembly having means for sensing and automatically shutting off flow offluid from the membrane enclosure if such flow becomes abnormally highor low, such as if a leak should occur, so that the system will not bedrained of fluid. This separator assembly comprises a semipermeablemembrane; means for passing fluid along one surface thereof; means fordrawing off fluid diffusate passing through the membrane to the othersurface thereof; valve means controlling flow of fluid diffusate; andflow-sensitive sensing means operatively associated with the valve meansand responsive to a predetermined change in diffusate flow rate and/ orviscosity to close the valve and thus stop diffusate flow.

The separator of the invention is particularly adapted for theseparation of air and other gases from liquids such as oil and hydraulicfluid, although it can also be used to separate liquids from liquids,and liquids from gases, and gases from gases.

The separator of the invention employs a thin semipermeable membrane.The membrane can be from about 0.0005 to about 0.005 inch thick. Thematerial of which the membrane is made is selected according to thematerial to be separated out by passage through the membrane. Forexample, if air is to be separated from oil or hydraulic fluid, anair-permeable oilimperrneable polytetrafluoroethylene membrane orfluorinated ethylene-propylene copolymer membrane is suitable.Water-impermeable air-permeable dimethyl silicone rubber membranes andsilicone polycarbonate copolymer membranes can be used for separatingoil from water. Water can be separated from oil or hydraulic fluid orfrom water having impurities therein, such as soluble salts or air, by awaterperrneable nylon membrane, a water-permeable regenerated cellulosemembrane, or other water-permeable membranes known to those skilled inthe art. In the case of separation of water from water solution, thepure water diffuses through the membrane under a positive fluid pressuredifferential, leaving the soluble salts in concentrated aqueous solutionon the other side of the membrane. Selected dissolved ionized materialscan also be removed by use of a cationor anion-permselective ionicmembrane.

The semi-permeable membrane is in the form of an enclosure having aspace therewithin for flow of diffusate to a discharge passage throughthe core. One form of enclosure is a closed envelope or pouch having twomembrane sheets bonded together on all four edges. A single rectangularsheet can be folded, and the three open edges sealed, to form anenvelope. It is possible to flatten a tubular membrane and seal the twoends, or to nest two concentrically tubular membranes, and then bondtheir ends so that the tubes define an annular enclosure.

The edges of the enclosure can be sealed by any means suitable to themembrane material. They can be solventbonded together, (if solventsoluble), heat-bonded together, (if thermoplastic), and adhesive-bondedtogether, such as by a resin. It is preferred, however, that a membranemade of a thermoplastic material be employed, and that the edges of themembrane enclosure be heat-bonded together to form a leaktight seal.

The open interior of the enclosure is preferably provided with a memberwhich spaces the membrane walls apart, and maintains an open flow spacefor passage within the enclosure of diffusate from the system. Thespacer is preferably made of coarse plastic mesh, which can be eitherwoven or extruded. A corrugated sheet material whose corrugations run inthe same direction as flow through the enclosure is useful. Any spacerwhich provides a high open flow space can be used.

The interior of the membrane enclosure communicates with the dischargepassage in the core, via openings formed in the membrane wall and in thecore. If one opening is insufficient to accomodate the flow, severalopenings or a long a narrow slot or groove can be used.

The core can have any cross-sectional shape, but the sealing surface towhich the membrane enclosure is attached must be flat. The corepreferably is cylindrical in cross section, except for the flat portion.

The core can be a hollow tube, or a solid rod or bar, in which a borecomprising the discharge passage is provided. The discharge passagepreferably runs axially in the core, to an end thereof. The dischargepassage can communicate with the opening in the flat portion of the coresurface via a connecting passage, but the discharge passage can becurved, or formed at an angle, so as to itself connect with the openingin the flat portion of the core surface.

The flat portion of the core can be a flat surface segment which extendslengthwise along the entire length of the core. However, the flatportion need not extend along the entire length of the core, but cancomprise only the sealing surface which surrounds the opening in fluidcommunication with the discharge passage. lf several openings areprovided, only the opening in fluid communication with the dischargepassage requires an abutting flat sealing surface, since the otheropenings can be made leaktight by sealing them off from the open spacewithin the enclosure. There can be non-apertured flat portions on thecore at different spaced locations along the length of the core, one foreach location at which the membrane is to be fixed to the core.

The flat sealing surface on the core is an important feature of theinvention. A flat sealing surface permits a secure and leaktight sealwith the flat membrane wall at the apertures, since a planar seal can beformed. The forces which generally tend to break the seal are shearforces, which normally occur in the plane in which the bonds are formed.However, if the force which holds the seal tight is distributed over aplanar surface, the adjacent portions of the seal tend to reinforce eachother so as to resist any shearing stresses which might otherwise tendto break the seal. This is to be compared with the essentially pointbonds which would occur on the surface of a cylinder or the like, whichare all in different planes, and which do not reinforce each othersignificantly against shear stresses. The flat surface also provides amating surface for flat washers.

The core can be made of metals such as aluminum, steel, stainless steel,nickel and nickel alloys, brass and the like. Plastic materials such ashard synthetic rubber,

polypropylene, polyvinyl chloride, polycarbonate, polyethylene,polystyrene, Viton-A, polyurethane, nylon, polytrifluorochloroethylene,and polytetrafluoroethylene can be used.

The core can be fixed to the membrane enclosure either before or afterthe edges of the membrane enclosure are sealed, depending on the meansemployed to fix the core to the membrane enclosure. For example, themembrane separator can be fixed to the core by mechanical means, such asone or more screws, one of which is hollow and communicates with theinterior of the core through the communicating openings in the core andin the membrane wall. If a single membrane sheet is used, this can bedone by placing a membrane sheet on the core, so that approximately halfof the sheet width extends beyond the end of the core. The sheet is thensecured to the core and is then folded in half, back upon itself, andthe edges sealed. Mechanical fasteners such as rivets, bolts, clips, andclamps can also be used in combination with washers to seal the membraneto the core.

The hole made by the mechanical fastener (other than the hollowfastener) is a potential source of leakage, even if leakresistantwashers are used to ensure a tight seal. To eliminate this, such holes,(other than that made for the hollow fastener) can be sealed off fromthe open flow-through space within the membrane enclosure by sealingboth sides of the membrane together, as by a heat-seal or solventbonding.

The membrane enclosure can also be sealed to the core, usingheat-sealing, solvent-bonding or an adhesive. Such sealing cansupplement or replace mechanical fasteners.

After the membrane enclosure is sealed to the core, the enclosure iswrapped or folded into a shape which provides a high membrane area in asmall volume. This can be done for example by winding membrane enclosurein a spiral about the core. The membrane enclosure, however, can befolded into a series of corrugations or convolutions. In each of theseinstances, it is preferred to place a second spacer between the adjacentwindings or corrugations to maintain an open flow space therebetween.These spacers can be a corrugated sheet, coarse mesh, or any othermaterial having a high open area.

In the preferred embodiment, a series of openings or apertures,preferably five, are provided in the membrane. The apertures arearranged in a row, in spaced positions, such that when the membrane isfolded over, the apertures will be aligned with a registering pair ofapertures provided at each side of the enclosure and a single apertureopening only to the inside of the enclosure intermediate the registeringpairs of apertures. The core has three aligned apertures withcorresponding abutting flat surfaces of which the middle one connectswith the discharge passage of the core.

It is to be noted that the core can be fixed to the membrane enclosureeither at a central location or at an end thereof.

In order to assemble the membrane and the core into a unit, the membraneis laid over the core, such that the three apertures in the coreregister with the three apertures in the membrane. A hollow screw with asealing washer is then placed through the middle aperture in themembrane which registers with the aperture in the flat sealing surfacecommunicating with the discharge passage. A coarse drainage memberhaving corresponding apertures is placed over the membrane, and themembrane is then folded over so that the remaining apertures in themembrane are aligned with each other. A screw and a plastic washer arethen inserted through each pair of registering apertures, and tightenedinto place, to fix the sheet to the core and seal it against leakage.The edges of the membrane are then sealed, to form the enclosure.

If a plastic core is used, the same procedure can also be employed.However, it is also possible to solventor heat-bond the enclosure to thecore, if the core is of the same as or a closely related material to themembrane material. The procedure for bonding the core to the membraneenclosure is similar to the above, with the exception that only oneaperture in the core and in the membrane enclosure is required. Themembrane can be bonded directly to the flat surface of the core, whilethe aperture in the enclosure is in registering position with theaperture in the core, so as to fix the membrane sheet to the core, andseal the enclosure to the core about the registering apertures toprevent leakage.

The composite of the core and the membrane enclosure coiled about it canbe fitted within a cylindrical container, so as to form a cartridge. Oneend of the cartridge can be provided with means such as an end cap forclosing off one open end of the cartridge, and supporting the cartridgein a leaktight fit in the housing. The other end of the remain open forinfluent flow.

This invention further provides a means for shutting off flow throughthe discharge port passage if a change in the magnitude or viscosity ofthe discharge flow occurs. This is important, if for example, a leak inthe membrane occurs, since the liquid being purified would pass throughthe membrane and proceed into the core and out the discharge passage. Ifthis were to occur and remained unchecked the system could be rapidlydrained of liquid. The shut-off device of the invention is provided toprevent this from happening. The shut-off device comprises aflow-sensitive sensing means associated with a valve positioned in thedischarge flow line. The valve is moveable between first and secondpositions. In its first position, the valve permits flow to pass throughthe discharge flow line, and in its second position the valve closes offthe line.

The valve moves between its first and second positions in response to achange in the magnitude or viscosity of the diffusate flow. This isaccomplished by a flow-sensitive sensing means. The flow-sensitivesensing means is operatively connected to the valve to open and closethe valve is response to flow changes. The flow-sensitive sensing meanscomprises a flow-responsive member such as a piston, a diaphragm, abellows or the like, having pressure surfaces exposed to and sensingboth upstream and downstream pressure, and a flowrestricting passagesuch as a capillary or narrow bore which is in the line of flow in thedischarge line, and communicates with the upstream and downstreampressure surfaces so that the flow responsive member is exposed to andthus senses any pressure differential created by flow through theflow-restricting passage. The flow-restricting passage makes theflowresponsive member sensitive to high flow volumes, and changes in theviscosity of flow. The flow-restricting passage provides a laminar flowpath through which the diffusate flow must pass. As it does so, apressure differential is created which is related to the magnitude andviscosity of the flow through the passage. The upstream and downstreamvalve surfaces are exposed to this pressure differential. A bias meanssuch as a spring is positioned so as to bias the valve away from itssecond position, so that fluid is free to flow through the dischargeflow line. The bias force acting on the valve is adjusted so that undernormal flow conditions this pressure differential is ineffective toactuate the valve, and thus the valve remains open and permits thisdischarge flow to pass through the discharge line.

If, however, an increase in flow volume or viscosity occurs, thepressure differential across the flow-restricting passage alsoincreases. When a sufficient predetermined pressure differential due toflow is reached, the bias force is overcome, and the valve moves intoits second position, in which it closes off flow through the dischargeline.

Other features of the invention which will apparent from the descriptionof the preferred embodiment of the invention, as shown in the drawings,in which:

FIG. 1 is a view partly in a cross section and partly broken away of aseparator in accordance with the invention,

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1,

FIG. 3 is an enlarged view in cross-section of the portion so marked ofFIG. 1, showing the shut-off mechanism,

FIG. 4 is a plan view of the membrane envelope of FIG. 1, showing how itis fixed to the core,

FIG. 5 is a view in cross-section taken along the line 55 of FIG. 4, and

cartridge can FIG. 6 is a view of the membrane envelope of FIG. 1,partially assembled to a core.

The membrane assembly shown in FIG. 1 comprises a housing 3 having ahead portion 4 and a bowl portion 5 threaded in the head portion. Thehead portion 4 has an inlet port 7, through which fluid to be purifiedcontaining membraneperrneable components enters the housing, and anoutlet port 8 through which the purified fluid leaves the housing. Theinlet port 7 leads into an inlet passage 9 which opens into the bowlportion 5, and the outlet port 8 is at the end of an outlet passage 10,which communicates with the bowl portion via a centrally formeddependent portion 12 of the head. The inlet passage 9 and the outletpassage 10 are connected directly via a bypass relief passage (notshown). Flow through this bypass passage is normally closed off by apressure-responsive relief valve 15 at the outlet end of the bypasspassage. This valve opens to permit flow to proceed through the bypasspassage whenever a predetermined pressure differential between the inletpassage 9 and the outlet passage 10 is reached.

Mounted in the bowl portion 5 is a separator 20 of the invention, whichcomprises a coiled semi-permeable membrane enclosure 21 (best seen incross-section by reference to FIG. 2) mounted on a core 18. The membraneseparator enclosure 21 is confined within a metal cylinder 22. The topend of this cylinder is closed off by an end cap 23, having a flange 25abutting a shoulder 19 on the dependent portion 12, to axially positionthe separator 20 in the bowl, and capture an O-ring 24. The O-ring 24seals against the dependent portion 12 of the housing, and therebyprevents fluid from bypassing the membrane separator assembly 20.

The bottom of bowl 5 is provided with a port 13 into which is threaded ashut-off valve assembly 55, which is described later. An O-ring 14 sealsthe assembly 55 against leakage from the bowl via port 13.

Membrane enclosure 21 is formed of two membrane walls 27 and 28 of aTeflon membrane 0.001 inch in thickness. A plastic mesh spacer 30between the layers 27 and 28 defines an interior flow space 37 betweenthe membrane walls into and through which the diffusate passes. One wall27 of the membrane enclosure 21 is fixed to a flat surface 16 formed onthe core 18, and the membrane enclosure is coiled about the core. Thewindings of the membrane enclosure are spaced apart by a corrugatedaluminum spacer 17, which defines flow channels 31 for fluid flow alongthe surfaces of the membrane.

Fluid entering the inlet port 7 passes through the inlet passage 9 anddown through the space 26 defined between the inside wall of the bowl 5and the cylinder 22, to the bottom open end 33 of the cylinder. Fluidthen passes into the coiled membrane separator assembly 20 in the openspaces 31 between the windings of the membrane enclosure 21.

The core 18 has a central discharge passage 32 formed therein (best seenin FIG. 3). The passage rungs lengthwise in the core, and terminates atone end thereof. The passage 32 also communicates with the flat sealingsurface 16 of the core via a bore 34 which terminates in an opening 35in the flat surface of the core, as can be seen in FIG. 5. The interiorflow space 37 of the membrane enclosure 21 communicates with opening 35via an opening 38, formed in the facing membrane wall 27.

The membrane enclosure is held to the core by three screws 40,43 whichpass through corresponding openings formed in the membrane walls. Thescrews fit into threaded bores 42, 34, in the flat surface 16 of thecore 18 and hold the enclosure 21 in position. The two end screws 40pass through pairs of openings 41 formed in the membranes walls 27 and28, and into bores 42 in the core. Teflon washers 45 are provided onboth sides of the membrane walls to prevent any possible leakage aroundthe screws when the screws are tightened. Additionally, the screws 40are isolated from the remainder of the membrane enclosure 21 by heatseals 51.

The intermediate screw 43 fits through the aperture 38 in the membranewall 27. This screw has a central passage 47 therethrough and isthreaded into the bore 34 which communicates with the central passage32. The screw 43 therefore communicates with the inside 37 of theenvelope, and the screw when tightened against the membrane 27 and theflat surface 16 of the core forms a leaktight seal between the membraneand the core. Thus, fluid from the interior of the membrane envelope canpass into and through the discharge end of the core via the centralpassage 47 in the screw 43, the bore 34, and the passage 32. Leakage isprevented in this case also by Teflon washers 45 positioned on each sideof the membrane wall 27.

The membrane enclosure is assembled on the core as follows withreference to FIGS. 4, 5, and 6. A rectangular sheet of membrane material27 is provided with four openings 41 and one opening 38, which arespaced such that when the membrane 27 is folded longitudinally in half,two pairs of openings 41 register with each other, and the remainingopening 38 is positioned intermediate the registering pairs of openings.Teflon washers are placed on the flat surface 16 over each of the bores42 and 34, and the membrane sheet 27 is then laid over the core suchthat two of the openings 41 and the opening 38 are in registeringpositions with the three bores 42, 34 in the core. The opening 38registers with the bore 34 in the flat surface and the openings 41 arein registering position with two of the bores 42. The screw 46 is thenplaced through a Teflon washer 45, and the washer and screw are thenplaced through the opening 38 in the sheet and threaded into the bore34. A mesh spacer sheet 30, which is just less than half of the width ofthe membrane (and just less than the width of the folded membrane) isthen placed over the portion of the membrane which is on the core, andthen the membrane is folded in half so that the remaining openings 41are in registering positions with the bores 42. Two screws 40 withTeflon washers 45 thereon are then placed through the pairs ofregistering openings 41 in the membrane, and are tightened against theflat surface of the core to firmly hold the membrane in position. A heatseal 50 is then formed across each open end of the membrane enclosureand another heat seal 52 is formed along the side edge of the membraneenclosure to complete the leaktight separator enclosure 21. A sheet ofcorrugated spacing material 17 is then placed over the membraneenclosure, and the composite is then coiled about the core and fittedwithin the cylinder 22, to form the membrane separator assembly 20. AnO-ring 46 is placed over the end of core 18. The assembly is then placedin the bowl with the end of the core 18 a port 29 of the valve assembly55 attached at the bottom of the bowl portion of the housing.

In operation, fluid to be purified enters the housing through the inlet7, passes through the inlet passage 9 into the space 26, and proceeds tothe bottom open end 33 of the separating assembly 20. The fluid theproceeds upwardly through the flow spaces 31 between the windings of thecoiled enclosure. As the fluid flows along the surface of the membranewalls 27 and 28 of the enclosure, the material to which the membrane ispermeable diffuses through the membrane. The fluid which does not passthrough the membrane leaves the assembly through the passage and theoutlet 8. The material which diffuses through the membrane walls flowsas diffusate into and through the flow space 37 between the walls 27 and28 of the enclosure 21, and passes through the passage 47 in the screw43 into the passage 32 in the core, and enters valve 55 via port 29.

If a blockage in the flow spaces 31 should occur, or fluid viscosityincreases, as in low temperature operation, the pressure differentialbetween the inlet 7 and the outlet 8 will increase. When the pressuredifferential reaches a predetermined maximum, the relief valve opens,permitting fluid to pass from the inlet directly to the outlet,bypassing the separator 20.

The shut-off valve assembly 55, mounted at the bottom of the bowl,comprises a housing 60 having a chamber 73 in which a flow-responsivepiston 65 is reciprocably movable. The bottom of the chamber 73 isformed with a well 80, and an outlet passage 88. The piston 65 is biasedby a spring 66 away from the well 80. The piston 65 has a peripheralsealing ring 76, which divides the chamber 73 into two parts 75 and 77.Port 29 carries diffusate flow to chamber section 75. The outlet passage88 carries flow from chamber section 77. A capillary passage through thepiston carries flow from chamber 75 via cross drilled hole 84 intochamber 77. The capillary passage 85 is dimensioned so as to provide alaminar flow path through the flow-responsive piston 65. A force occursacross piston 65 as a result of the pressure differential produced bythe fluid passing through the passage 85. The spring 66 under normalconditions offsets this force and therefore prevents the piston 65 frommoving into its seated position in well 80.

The valve stem 86 on the bottom of the piston 65 is encircled by sealingring 87. In the open position shown, an annular space 89 is left betweenthe stem 86 and the edge of the well 80, through which flow proceeds tothe outlet passage 88.

The valve stem 86 and the sealing ring 87 are adapted to movereciprocably into and out of the well 80, depending on the flow throughthe valve 55. The well 80 constitutes a valve seat, so that the ring 87forms a tight seal against the walls of the well 80. This prevents fluidfrom passing from the chamber 77 to the outlet passage 88 when the stem86 moves into the well 80. The outlet passage 88 communicates with afitting 90 (see FIG. 1) for a connection to the atmosphere. An orifice92 is provided in the fitting so as to ensure a back pressure in theassembly and prevent false actuation of the valve when exhausting to lowabsolute pressure. A filter (not shown) protects orifice 92 fromplugging.

In operation, under normal conditions diffusate discharged from theseparator proceeds from port 29 into and through chamber 75, capillary85, and hole 84, into the chamber 77. Diffusate then proceeds throughthe annular space 89, well 80 and outlet passage 88, orifice 92, andfitting 90. If the diffusate flow rate or viscosity increases, the forceacross piston 65 increases as a function of the increased flow rate orviscosity. When the force reaches a predetermined value, and exceeds theforce of the spring 66, the piston 65 moves the stem 86 and the sealingring 87 into the well 80, to close off the annular space 89, therebyshutting off the flow to the outlet passage 88.

The above separator is particularly useful in the separation of air fromoil or hydraulic fluid. Normally, the air and a small amount of liquidpasses through the membrane and the shutoff valve 55 is sized toaccumulate this normal flow of fluid without shutting off. if the fluidflow increases abnormally, such as if the membrane breaks, the valve 55senses the increased liquid flow (as opposed to gas flow) and shuts offflow, preventing further loss of liquid and thus preventing drainage ofthe oil or hydraulic fluid from the system.

What is claimed is:

1. A semipermeable membrane separator comprising, in combination, asemipermeable membrane sheet in the form of an enclosure having a spacetherewithin for flow of material passing through the membrane and anopening therein in fluid communication with the space; a supporting corefor the membrane enclosure, the core having an external flat portion ona surface thereof to which the membrane sheet in the portion surroundingthe opening is attached in a leaktight seal flat against the externalsurface of the core and in the plane of the core; and a fluid passage inthe core in fluid communication via the opening in the membraneenclosure with the space within the membrane enclosure for discharge ofmaterial therefrom that passes through the membrane into the membraneenclosure.

2. A separator in accordance with claim 1, in which the membraneenclosure is secured to the core by a screw passing through the membranesheet and sealed off from the space within the membrane enclosure toprevent leakage.

3. A separator in accordance with claim 2, in which the membraneenclosure communicates with the core via a screw having a centralpassage therethrough.

4. A separator in accordance with claim 1, in which the membraneenclosure has a spacer therein.

5. A separator in accordance with claim 1, in which the membraneenclosure is wound about the core.

6. A separator in accordance with claim 5, in which the windings of themembrane enclosure are separated by a spacer.

7. A separator in accordance with claim 6, in which the spacer iscorrugated.

8. A separator in accordance with claim 1, in which the membrane sheetmaterial is folded to form a membrane enclosure having one folded sideand three open sides and heat sealed together at its three open sides toform the membrane enclosure 9. A separator in accordance with claim 1,in which the membrane enclosure is sealed to the flat portion of thecore surface by a fastener having a passage therethrough, said passageconnecting the interior of the enclosure with the discharge passage inthe core.

10. A separator in accordance with claim 1, in which the membraneenclosure is sealed to the flat portion of the core surface by anadhesive. 7

11. A separator in accordance with claim 1, in which the membraneenclosure is heat sealed to the flat portion of the core surface.

12. A separator in accordance with claim 1, in which the membraneenclosure is solvent-sealed to the flat portion of the core surface.

13. A separator in accordance with claim 1, in which the core has anaxial flow passage and a radial flow passage in fluid communicationtherewith and terminating in an opening in the flat portion of the corecommunicating with the opening in the membrane enclosure andcommunicating the interior of the enclosure with the axial core passage.

14. A separator in accordance with claim 1, comprising a housing havinga fluid inlet, a fluid outlet, and a discharge port formembrane-permeable material; and a cannister supporting a separator inaccordance with claim 1, and positioned in the line of fluid flow fromthe inlet to the outlet, such that fluid entering the housing enters thecannister via the fluid inlet and flows along the membrane enclosure,fluid that does not flow through the membrane proceeding to the outlet,while membrane-permeable material diffuses through the membrane into thespace within the membrane enclosure and thence through the openingtherein for discharge from the assembly via the core passage anddischarge port.

15. A separator assembly in accordance with claim 14, including meansfor shutting off flow through the discharge port if a predeterminedincrease in viscosity or flow volume occurs.

16. A separator in accordance with claim 1, comprising valve meansassociated with the core passage and controlling diffusate flow ofmembrane-permeable and controlling diffusate flow of membrane-permeablematerial.

17. A separator in accordance with claim 16, comprising flow-sensitivesensing means operatively associated with the valve means and responsiveto a predetermined change in diffusate or viscosity flow volume to closethe valve and stop diffusate flow.

18. A separator assembly in accordance with claim 17, in which theflow-sensitive sensing means comprises a flowrestricting passage and aflow-responsive member having pressure surfaces exposed to the pressuredifferential through the passage.

19. A separator assembly in accordance with claim 18, in which the flowrestricting passage is a capillary passage con necting the pressuresurfaces of the flow-responsive member.

20. A separator assembly in accordance with claim 18, in which oneflow-responsive member is a piston associated with the valve means, andbias means holding the valve in an open position until the flow volumeor viscosity exceeds a predetermined maximum.

21. A separator in accordance with claim 16, comprising an orifice inthe passage in the core, adapted to prevent false actuation of the valvemeans when exhausting to low absolute pressures.

2. A separator in accordance with claim 1, in which the membraneenclosure is secured to the core by a screw passing through the membranesheet and sealed off from the space within the membrane enclosure toprevent leakage.
 3. A separator in accordance with claim 2, in which themembrane enclosure communicates with the core via a screw having acentral passage therethrough.
 4. A separator in accordance with claim 1,in which the membrane enclosure has a spacer therein.
 5. A separator inaccordance with claim 1, in which the membrane enclosure is wound aboutthe core.
 6. A separator in accordance with claim 5, in which thewindings of the membrane enclosure are separated by a spacer.
 7. Aseparator in accordance with claim 6, in which the spacer is corrugated.8. A separator in accordance with claim 1, in which the membrane sheetmaterial is folded to form a membrane enclosure having one folded sideand three open sides and heat sealed together at its three open sides toform the membrane enclosure.
 9. A separator in accordance with claim 1,in which the membrane enclosure is sealed to the flat portion of thecore surface by a fastener having a passage therethrough, said passageconnecting the interior of the enclosure with the discharge passage inthe core.
 10. A separator in accordance with claim 1, in which themembrane enclosure is sealed to the flat portion of the core surface byan adhesive.
 11. A separator in accordance with claim 1, in which themembrane enclosure is heat sealed to the flat portiOn of the coresurface.
 12. A separator in accordance with claim 1, in which themembrane enclosure is solvent-sealed to the flat portion of the coresurface.
 13. A separator in accordance with claim 1, in which the corehas an axial flow passage and a radial flow passage in fluidcommunication therewith and terminating in an opening in the flatportion of the core communicating with the opening in the membraneenclosure and communicating the interior of the enclosure with the axialcore passage.
 14. A separator in accordance with claim 1, comprising ahousing having a fluid inlet, a fluid outlet, and a discharge port formembrane-permeable material; and a cannister supporting a separator inaccordance with claim 1, and positioned in the line of fluid flow fromthe inlet to the outlet, such that fluid entering the housing enters thecannister via the fluid inlet and flows along the membrane enclosure,fluid that does not flow through the membrane proceeding to the outlet,while membrane-permeable material diffuses through the membrane into thespace within the membrane enclosure and thence through the openingtherein for discharge from the assembly via the core passage anddischarge port.
 15. A separator assembly in accordance with claim 14,including means for shutting off flow through the discharge port if apredetermined increase in viscosity or flow volume occurs.
 16. Aseparator in accordance with claim 1, comprising valve means associatedwith the core passage and controlling diffusate flow ofmembrane-permeable and controlling diffusate flow of membrane-permeablematerial.
 17. A separator in accordance with claim 16, comprisingflow-sensitive sensing means operatively associated with the valve meansand responsive to a predetermined change in diffusate or viscosity flowvolume to close the valve and stop diffusate flow.
 18. A separatorassembly in accordance with claim 17, in which the flow-sensitivesensing means comprises a flow-restricting passage and a flow-responsivemember having pressure surfaces exposed to the pressure differentialthrough the passage.
 19. A separator assembly in accordance with claim18, in which the flow restricting passage is a capillary passageconnecting the pressure surfaces of the flow-responsive member.
 20. Aseparator assembly in accordance with claim 18, in which oneflow-responsive member is a piston associated with the valve means, andbias means holding the valve in an open position until the flow volumeor viscosity exceeds a predetermined maximum.
 21. A separator inaccordance with claim 16, comprising an orifice in the passage in thecore, adapted to prevent false actuation of the valve means whenexhausting to low absolute pressures.